Chemical and Physical Notes 127 



2 mm. The wind fell very light, and the thermometer remained at 8'o, 

 when the wind returned it fell to 5'8. The axis of the thermometer bulb 

 would be about 5 mm. from the ice, and still the air is nearly 6 warmer 

 than the ice. Another observation in the same conditions gave $*$. The 

 wet bulb was now exposed, but it had to be kept about 5 mm. off the ice ; 

 it showed 3'2. At 2.43 p.m. a great volume of warm air came down, and 

 the wet bulb ran up to 4'5 in three or four seconds. With the return of 

 the breeze the wet bulb went back to 3x>. The Fbhn puffs were now very 

 troublesome. At 2.52 p.m. the wet bulb at i m. was 7'o; the dry bulb 

 showed at 2.54 p.m., n-o; at 2.55 p.m., i3'5; and at 2.57 p.m., I4'5. 

 In one puff the thermometer was observed to rise one degree in eight 

 seconds, which would make the true temperature of the air at the moment 

 about 6'o higher, or I9'5. 



"At 3.30 p.m. I returned to the land stations, and again found the 

 same variable temperatures. Between 3.35 and 3.45 p.m. the tempera- 

 ture varied between i6x> and I3'5. The following averages were 

 taken : 



3.45 p.m., dry, i4'3; wet, 8 0> o; relative humidity, 35. 

 4-0 ,, i4 0l o; 8's; 42-5. 



" Taking the first of these and the observations at i o'clock, we have 

 for the mean temperature of the air I4'i5, and the wet bulb 775- On 

 the ice we have : 



At i metre, dry bulb, 9'85 ; wet, 5'6, and 



At 2 centimetres, ,, 7'3 ; ,, 4'o. 



" The difference in the temperature of the air at i m. is only 4'3, and 

 that between i centimetre and 2 metres above the ice is only 2 0> 55, while 

 the air at 2 centimetres is 7'3 warmer than the ice. 



"On the 22nd August the observations on the ice were repeated, with 

 very much the same results. The temperature of the air ranged from 9*o 

 to 9'5 at i metre, and was 5*5 at i centimetre from the ice. 



" The result of the few observations here quoted is to show that the 

 air, which over land has a temperature of 15 to 20, or higher, in passing 

 over a glacier is cooled to a comparatively slight degree. Although the 

 air appears to be thoroughly mixed by its own motion, very sharp 

 gradients of temperature are produced and maintained. The great and 

 abnormal temperature of the air of the valley is kept up by the heat 

 liberated by the compression accompanying the descent of local streams 

 or stria? of air from high levels. These keep up an extra supply of heat 

 over and above what is supplied by the direct radiation of the sun. The 

 result is that the melting of the glacier in Fohn weather greatly exceeds 

 that of even the hottest day of ordinary weather. 



"In order to convey a general idea of the climate in the neighbourhood 

 during the period when my observations were made, I subjoin a table of 



